Large quantities of waste water are generated in many industrial processes which waste water must be treated to remove various contaminants prior to discharge or recycle. For example, in the paper making industry about 15,000 to 20,000 gallons of process water are required to produce one ton of paper. About 70% of the waste water generated in the paper making process is so-called "white water" which contains a variety of contaminants such as finely divided suspended solids, e.g., cellulose fibers and clays as well as retention aid residues such as long chain fatty acids, organic polymers and the like. White water typically has a milky, opaque appearance, although it could contain various other color bodies depending on the presence or absence of dyestuffs in the various paper coating compositions.
Prior to disposal, or as is more typical, recycle and reuse, the white water must be first purified to remove all or a substantial portion of the various contaminants contained therein. Environmental considerations require removal of contaminants prior to discharge to a receiving stream whereas processing considerations require removal of contaminants prior to recycle and reuse to prevent build-up of contaminant concentrations which adversely effect the finished paper product.
Various sorption agents such as activated carbon and surface modified clay minerals have been used to remove such contaminants from aqueous systems. In accordance with this invention, it has been discovered that amorphous, precipitated silica which has had its surface modified with an organic quaternary amine is suitable for removing contaminants such as finely divided suspended matter, color bodies and dissolved organic residues from aqueous liquids such as the white water generated in a paper making process. This invention also provides a method of making said surface modified amorphous, precipitated silica.